Analyst readout for executives and security teams
Plain-English summary
CVE-2026-9939 is a high-severity Chrome flaw in WebCodecs. A malicious HTML page could let an attacker run code inside Chrome’s sandbox on vulnerable versions. Because exploitation requires user interaction and the source bundle shows no KEV listing, urgency is high but not confirmed as actively exploited.
Executive priority
Patch promptly in the normal emergency browser-update lane. The business risk is credible remote code execution through web content, but current evidence does not prove active exploitation or sandbox escape.
Technical view
The issue is a CWE-122 heap buffer overflow in Google Chrome WebCodecs before 148.0.7778.216. CVSS 3.1 is 8.8 with network attack vector, low complexity, no privileges, and required user interaction. Reported impact is arbitrary code execution inside a sandbox via crafted HTML.
Likely exposure
Organizations are likely exposed where managed or unmanaged desktop Chrome installations remain below 148.0.7778.216. Exposure is browsing-driven, so normal user web activity can create risk if users reach attacker-controlled or compromised HTML content.
Exploitation context
The provided sources describe remote code execution inside a sandbox via crafted HTML. They do not state active exploitation, weaponized public exploit availability, or CISA KEV inclusion. Treat exploit status as unconfirmed based on the bundle.
Researcher notes
Public detail is limited in the supplied bundle. The key confirmed facts are component, bug class, affected pre-fix Chrome version, CVSS vector, and crafted HTML trigger. Avoid assuming sandbox escape, broader Chromium product impact, or exploit availability without additional vendor evidence.
Mitigation direction
- Update Google Chrome to 148.0.7778.216 or later.
- Prioritize managed desktop Chrome fleets and high-risk user groups.
- Confirm browser auto-update policies are enabled and enforced.
- Check Google Chrome release guidance for any additional vendor instructions.
Validation and detection
- Inventory Chrome versions across endpoints.
- Flag systems running Chrome versions before 148.0.7778.216.
- Verify updated endpoints report the fixed version or later.
- Review browser management telemetry for failed or deferred updates.
Public sources used
Based on public source material and reviewed before publication.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-122: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupExecution behavior lookup
The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2026-9939 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.8 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
SSVC decision data
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H 2.8 5.9 CISA-ADP Vulnerability scoring details
Base CVSS 3.1 score
8.8 HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reserved CVE Program
The CVE ID was reserved by the assigning CNA.
- CVE published CVE Program
The CVE record was published.
- CVE updated CVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 source CVE List V5
- https://chromereleases.googleblog.com/2026/05/stable-channel-update-for-desktop_0877304591.html CVE reference, Chrome
- https://issues.chromium.org/issues/502735235 CVE reference, Chrome
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Heap-based Buffer Overflow
Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.